1. Field:
The invention is in the field of bacteriophage prevention and control of harm to plants caused by bacteria, for example bacterial diseases in plants and bacterial promotion of frost.
2. State of the Art:
Although the use of bacteriophages (viruses) against bacterial plant diseases has been proposed in the past, any significant application of such proposal has not taken place. This is due largely to the well recognized tendency for the development of bacterial mutants resistant to the viruses employed. Plant pathologists, who are normally relied upon to diagnose and treat plant diseases, have rejected the use of bacteriophages (usually and hereafter referred to simply as "phages") as a practical matter primarily because there has been no way to combat the virus-resistant mutants.
Kozloff and Schnell were granted a patent (U.S. Pat. 4,375,734) in 1983 to protect plants against frost injury by using a specific wild-type phage that inhibits the ice-nucleation bacterium Erwinia herbicola. They sprayed corn plants grown in a greenhouse, some with suspensions of E. herbicola in a phosphate buffer solution, some whith buffer only, and others with a virus Erh 1 in buffer. These were compared as controls with another group of plants that were wetted with E. herbicola in phosphate buffer and allowed to stabilize for 24 hours before treatment with Erh 1 in buffer. Plants treated with E. herbicola in buffer alone sustained greater than 95% frost damage, whereas those treated with buffer only and phage in buffer exhibited no statistically significant frost injury. The plants treated first with E. herbicola and then phage Erh 1, showed 20-25% less damage than those sprayed only with E. herbicola. When Kozloff and Schnell added phage Erh 1 to a culture of E. herbicola, the bacterial population was drastically reduced in two hours but 10% were not killed. I presume that, these were bacterial mutants resistant to Erh 1. To my knowledge, Kozloff et al.'s teachings are still a laboratory curiosity and have not been applied commercially.
In connection with my work on a doctoral thesis in the field of microbial genetics, with research emphasis on the molecular structure of bacterial cell walls, I used phages as a research tool and came across the discovery by S. E. Luria, Indiana University, as published in Genetics, Vol. 30, pp. 84-99, Jan. 1945, of the existence of viral mutants that will attack Escherichia coli mutant bacteria which are resistant to the parent virus. Although E coli bacteria are normal inhabitants of the intestinal tracts of animals and do not cause diseases in plants, I conceived of the possibility that there might be viral mutants that would attack virus resistant mutants of bacteria that cause plant diseases, frost damage, or other harm. Sometime later, I was called upon to serve as a microbiological consultant to a major bean seed producing company, and I proposed to its plant scientists that this concept be tested. There appeared to be a lack of understanding of what I was proposing, so the concept was presented to molecular biologists at a genetic engineering company. It was evaluated as having only a minimal chance of being successful. However, I have subsequently shown that it is successful.